Typical foot operated crank systems allow leg motion to be converted to rotational motion. The standard design mounts foot pedals at the end of crank arms at opposite ends of an axle. A sprocket is usually fastened to the axle to engage a roller chain which transfers the rotary motion to a rear wheel, in the case of a bicycle, or other driven device for other prior art applications.
For low friction, the axle is mounted for near effortless rotation in roller bearings. The roller chain must also be kept in exact alignment with the drive sprocket to insure against power robbing drag and derailment. Since the rear wheel and its sprocket are adjustable, and since bicycle frames may be slightly bent, the pedal driven sprocket should be adjustable to maintain chain alignment. Several solutions to this requirement have been tried in the prior art.
Some designs place fixed thickness washers between the bicycle frame and the axle bearing retainers to shift the axle in crude steps that only approximate the correct chain alignment. This requires removal of the crank arms, taking the axle out of the frame, switching washers, and reassembling the entire collection of parts several times to search for the best alignment in a clumsy trial and error approach. Other designs uses a separate sealed bearing assembly. The entire assembly is mounted in a threaded hole in the bicycle frame, with threaded rings at each end, so that the entire assembly can be threaded axially to the desired position. But the crank arms must be removed to put a wrench on the threaded rings and the sealed bearings can not be replaced or maintained. Repair necessitates throwing away the entire bearing assembly, axle and all.
Still another prior art design uses a sleeve about the center of the axle that rests against the inner faces of the bearings. The sleeve may be locked to the axle with a set screw or snap rings. But again, adjustment requires complete disassembly of the bearing. The present invention avoids the above described problems as described hereinafter.